Existing dimmers use the common power line to provide dimming information to the light source by cutting the phase. These so-called phase cut dimmers can be used to dim existing halogen or incandescent light bulbs and in the future also LED based light sources. With the rise of LEDs in general lighting, there exists the need to also adjust the color point, color per se and/or color temperature, of the light emitted by the LED light sources. For example from U.S. Pat. No. 5,803,579, already discloses a tunable LED light source, where the color temperature of the LED light source can be adjusted. The proposed solution uses the mains power line to communicate the color temperature information from the user interface, i.e. a switch or dimmer, to the LED. For transferring this information, digital information is modulated onto the power line according to a proprietary protocol. Furthermore, the communication is a serial communication, where the information is transmitted over the power line from the control point, i.e. the light switch, to the lamp bulb in a serial fashion.
The known solution has the disadvantage that the digital communication requires each lamp to be configured with a dip-switch, in order to know, whether it is addressed or not. Further, the proprietary lamp driver will not work with a common phase cut dimmer. Consequently, this requires that both the lamp and the dimmer need to be replaced at the same time. Furthermore, the serially controlled LED light sources will not work with existing phase cut dimmers.
Therefore, there is a need for a compatible solution for setting the color point of a lighting device. There is further the need for providing the possibility to provide dimming of light intensity while also setting the color point information using the common driving voltage, i.e. the power line.